It beckons buyers with translucent Aero Glass 3-D window displays, the promise of faster boot ups, more reliability, and stouter protection against viruses and spam. But is the new Windows Vista operating system (OS), a great leap forward or the last big splash as computing migrates to the Internet and away from PC-based software? Either way, one study predicts the software will be installed on as many as 90 million computers worldwide by the end of 2007.

Five years in the planning, Vista promises to turn older PCs (if they can handle the heavy technical specs) and new ones into sleek, slick user-friendly environments. Versions for business use are now on the market. Basic and premium versions for consumers will be available at the end of January.

Realizing that they would miss the lucrative Christmas selling season this year, Microsoft and computermakers are offering holiday buyers coupons giving them a free upgrade to Vista when it hits the market.

But retailers seem to have put selling "Vista ready" machines and the coupon program on a back burner and are concentrating on slashing PC prices to rack up December sales, says Toni Duboise, a senior analyst at Current Analysis, a tech research firm in Sterling, Va. Ironically, Ms. Duboise says, "Most consumers really didn't know about Vista until [Microsoft] announced that it wasn't going to come [before Christmas]."

Vista has had a higher profile with tech-savvy, high-end buyers who want the latest. But even some of them are likely to give in to holiday bargains and buy now, waiting to "deal with Vista when it comes out," Duboise says.

With Vista almost certain to become the dominant OS inside the world's PCs well into the next decade, missing the Christmas sales season this year is an "almost insignificant" part of its overall impact, says Michael Gartenberg, a senior analyst at JupiterResearch in New York, which follows consumer technology trends.

"This is a major, major upgrade," Mr. Gartenberg says, "Microsoft's best work to date in terms of an operating system." Users will find that in the Vista environment, "Things flow much more naturally," he says. "It feels like a much more holistic and polished experience."

According to Forrester Research in Cambridge, Mass., the OS that Vista is replacing, Windows XP (introduced in 2001), took more than four years to be installed on a majority of PCs. Today it still occupies only 76 percent of the PC market. Older versions of Windows, such as Windows 2000, make up most of the rest.

Forrester predicts Vista will be adopted at a similar or slightly faster rate than was XP. Twelve million American households will have Vista by the end of 2007, Forrester says, and 73 million by the end of 2011.

Vista's impact is bound to reverberate throughout the world of PCs as new hardware and software takes advantage of its capabilities, analysts say. Every dollar that businesses and consumers spend on Vista is expected to create $18 in revenue for related products and services, predicts a Microsoft-sponsored report from tech research firm IDC.

In the years ahead, nearly all PCs will migrate to Vista as Microsoft drops its support for earlier Windows operating systems, says Ben Gray, a Forrester analyst.

Early sales are expected to come mostly from consumers. Businesses are notoriously slow to adopt a new OS. A Forrester survey of more than 450 North American enterprises earlier this year found 11 percent said they would switch to Vista within six months of its release and 29 percent within a year. But 60 percent said they either would wait longer than that or had no plans to switch at all.

Because businesses must test how their own applications work on Vista, it could take them six to 18 months to get ready to deploy, Mr. Gray says.

PC owners will be able to buy a copy of Vista to install on their current computer. But the computer will have to be "Vista ready" – most likely a fairly new machine with plenty of memory and other robust technical specifications. To add to the confusion, four versions will be available – Home Basic, Home Premium, Business, and Ultimate – each with its own set of features and requirements. Microsoft's Vista website offers advice (microsoft.com/windowsvista /getready) that can help determine which version, if any, an existing computer will be able to run.

Anyone installing Vista will have to be computer savvy. "I wouldn't advise a Vista install," Duboise says, calling the process something "not for the faint of tech heart." But Gartenberg is less daunted. "We're dealing with a pretty sophisticated digital consumer these days," he says, "and I don't expect it's going to be a huge issue."

A survey of computer sales last month by Current Analysis found that about one-third of the laptops and about 60 percent of the desktops sold would be able to run Vista Premium.

Half of the PCs in use by businesses today can't run any version of Vista, and 94 percent can't run Vista Premium, says a report from Softchoice Corp. Though Vista Basic should operate with 512 megabytes of system memory, for example, 1 or 2 gigabytes is recommended for Vista Premium, the version that displays the most innovative aspects of the new operating system.

"If you want to experience what Vista is all about, you want to go to the Premium," Duboise says.

Earlier this month, Gartner Inc. predicted that Vista would be the last big release of a new Windows operating system by Microsoft. "The next generation of operating environments will be more modular and will be updated incrementally," the research firm said in a forecast for 2007. "The era of monolithic deployments of software releases is nearing an end. Microsoft will be a visible player in this movement, and the result will be more flexible updates to Windows and a new focus on quality overall."

But both Duboise and Gartenberg see major Windows releases still ahead. The era of "software as a service," not on your PC, is not here yet.

"People have been saying for 10 years that the operating system is irrelevant, and everything is coming through the Internet," Gartenberg says. "Yet more and more is still being done through the operating system."